<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>02_流程控制</title>
</head>
<body>
    <script>
        //1.顺序结构
        console.log(1);
        console.log(2);
        console.log(3);
        //2.分支结构
        let username = '';
        if(!username){
            alert('用户名不能为空!');
        }else{
            alert('欢迎'+username+'回归!');
        }
        //3.选择分支
        let gender = 10;
        switch (gender) {
            case 1:
                console.log('男');
                break;
            case 2:
                console.log('女');
                break;
            default:
                console.log('未知');
        }
        //4.循环结构
        let names = ['张三','李四','王五'];
        for(var i=0;i<names.length;i++){
            console.log(names[i]);
        }
        //如果用var定义变量，则i在循环结束后，任然存在
        console.log(i);
        //增强for循环
        //let n 表示当前便利到的元素
        for(let n of names){
            console.log(n);
        }
    </script>
</body>
</html>






























